As previously described, the gearbox should be filled with engine oil, and the level of oil should be checked from time to time. After the first 500 miles with a new machine, drain all the oil out of the gearbox and refill the gearbox with fresh oil. If it is desired to do so, the gearbox may be flushed out with clean petrol. In normal service the gearbox oil should be changed every 1,000 miles—no other attention is necessary, but it cannot be too strongly emphasized that ordinary engine oil is the only lubricant which should be used. Heavy gear oil or grease will not find their way to the various bearings in a satisfactory manner and may involve some part running dry with the consequent risk of seizure.